Syntheses, crystal structures, Hirshfeld surface analyses and energy frameworks of two 4-aminoantipyrine Schiff base compounds: (E)-4-{[4-(diethylamino)benzylidene]amino}-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one and (E)-4-[(4-fluorobenzylidene)amino]-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one

The title 4-aminoantipyrine Schiff base compounds both deviate from planarity with the phenyl ring and the substituted benzylidene ring being inclined to the pyrazole ring mean plane by 54.87 (7) and 22.92 (7)°, respectively, in the first compound and by 60.44 (8) and 12.70 (9)° in the second.


Structural commentary
The molecular structures of I and II are illustrated in Figs. 1 and 2, respectively. Selected geometric parameters for I and II and their analogues are given in Table 1. The various dihedral angles in the five compounds are given in Table 2. The configuration about the N3 C12 bond is E, which favours the presence of an intramolecular C12-H12Á Á ÁO1 hydrogen bond in both compounds (Tables 3 and 4,  A view of the molecular structure of I, with atom labelling. The displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view of the molecular structure of II, with atom labelling. The displacement ellipsoids are drawn at the 50% probability level. Table 1 Selected geometric parameters (Å , ) for I and TAYLUB01 a , and for II and KELZIL b and KEQXOU c .   (7) , respectively, in I and by 60.44 (8) and 12.70 (9) , respectively, in II. The latter two rings, B and C, are inclined to each other by 73.98 (6) in I and by 71.28 (8) in II. The difference in the conformation of the two structures is illustrated in Fig. 3 showing the structural overlap (Mercury; Macrae et al., 2020) of molecules I and II. It can be seen from Table 2 that the conformation of I is similar to that of the 4-(dimethylamino)benzylidene analogue (TAYLUB01). However, this is not the case for compound II: while the conformation of the 4-(chloroamino)benzylidene (KELZIL) and 4-(bromoamino)benzylidene (KEQXOU) analogues of II are similar there is a significant difference compared to the conformation of compound II. For example, the A to B dihedral angle is 60.44 (8) in II but is 51.6 (1) and 50.8 (2) , in the respective analogues. The other dihedral angles are also significantly different, as seen in Table 2. The N1 and N2 nitrogen atoms of the pyrazole ring have pyramidal geometries (see Table 1), with the sum of their bond angles being 350.5 (1) and 341.5 (1) , respectively, in I, and 348.2 (1) and 351.0 (1) , respectively, in II. The same pyramidal geometries of atoms N1 and N2 are also observed for the various analogues (Table 1). The bond angles involving atoms N1 and N2 follow the same pattern.

Supramolecular features
In the crystal of I, the molecules are linked by C-HÁ Á ÁO hydrogen bonds, forming slabs lying parallel to the ab plane. The slabs are consolidated by C-HÁ Á Á interactions (Table 3 and Fig. 4).
In the crystal of II, the molecules are linked by C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds forming undulating slabs lying    A view along the b axis of the crystal packing of I. The C-HÁ Á ÁO hydrogen bonds are shown as dashed lines and the C-HÁ Á Á interactions as blue arrows (see Table 3). Only the H atoms involved in these interactions have been included. Table 3 Hydrogen-bond geometry (Å , ) for I.

D-HÁ
parallel to the ac plane. Here too, the slabs are strengthened by C-HÁ Á Á interactions (Table 4 and Fig. 5).

Hirshfeld surface analysis and two-dimensional fingerprint plots
The Hirshfeld surface analyses and the associated twodimensional fingerprint plots were performed with Crystal-Explorer17 (Spackman et al., 2021) following the protocol of Tan et al. (2019). The Hirshfeld surfaces (HS) of I and TAYLUB01 are compared in Fig. 6, and those for II and KELZIL and KEQXOU are compared in Fig. 7  A view along the b axis of the crystal packing of II. The The C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds are shown as dashed lines and the C-HÁ Á Á interactions as blue arrows (see Table 4). Only the H atoms involved in these interactions have been included.

Figure 6
The Hirshfeld surfaces of compounds, (a) I and (b) TAYLUB01 mapped over d norm in the colour ranges À0.2834 to 1.4293 and À0.2505 to 1.2511 au., respectively.

Energy frameworks
A comparison of the energy frameworks calculated for I and II, showing the electrostatic potential forces (E ele ), the dispersion forces (E dis ) and the total energy diagrams (E tot ), are shown in Fig. 10. The energies were obtained by using wave functions at the HF/3-2IG level of theory. The cylindrical radii are proportional to the relative strength of the corresponding energies (Spackman et al., 2021;Tan et al., 2019). They have been adjusted to the same scale factor of 90 with a cut-off value of 6 kJ mol À1 within a radius of 6 Å of a central reference molecule. It can be seen that for all five compounds the major contribution to the intermolecular interactions is from dispersion (E dis ), reflecting the absence of classical hydrogen bonds in the crystals. The colour-coded interaction mappings within a radius of 6 Å of a central reference molecule and the various contributions to the total energy (E tot ) for compounds I and II are given in Figs. S1 and S2 of the supporting information.

Database survey
A search of the CSD (CSD, Version 5.43, last update November 2022; Groom et al., 2016) for benyzylidene-substituted 4-aminoantipyrine organic structures with R 0.05, no disorder, no ions, single-crystal analyses only gave more than 90 hits. In all compounds the configuration about the C N bond is E. Various geometrical parameters of these compounds where analysed using Mercury (Macrae et al., 2020) Table 5 Principal percentage contributions of inter-atomic contacts to the Hirshfeld surfaces of I, TAYLUB01 a , II, KELZIL b and KEQXOU c .

Figure 10
The energy frameworks calculated for I viewed along the b-axis direction and II viewed along the a-axis direction showing the electrostatic potential forces (E ele ), the dispersion forces (E dis ) and the total energy diagrams (E tot ).
1.297 Å with a mean value of 1.281 Å (mean s.u. 0.008 Å ). For compounds I and II and their analogues this bond length varies from 1.276 (2) Å for KELZIL (Sun et al., 2006) to 1.291 (2) Å for I (see Table 1), well within these limits. The C-N-N bond angles within the pyrazole ring vary from ca 107.7 to 110.7 with a mean value of 109.3 (mean s.u. 0.5 ). The same angles in the title compounds (i.e. C1-N1-N2 and C3-N2-N1) and their analogues vary from 106.9 (3) in KEQXOU (Yan et al., 2006) to 109.58 (9) in I for the former and 106.23 (9) in I to 107.7 (3) in KEQXOU for the latter. The nitrogen atoms of the pyrazole ring have pyramidal geometries in all structures.

Synthesis, crystallization and spectroscopic analyses
Diethylaminobenzaldehyde (9.08 mmol, 1.744 g) and 1,5dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (9.08 mmol, 2.00 g) were added to 100 ml of methanol and the mixture was refluxed at 353 K for a period of 8 h. The solvent was then allowed to evaporate slowly at room temperature. Pale-yellow crystals of compound I were obtained after a period of three weeks. Melting point 492 K. 4-Fluorobenzaldehyde (9.80 mmol, 1.221 g) and 1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (9.80 mol, 2.00 g) were added to 100 ml of methanol and the mixture was refluxed at 353 K for a period of 8 h. The solvent was then allowed to evaporate slowly at room temperature. Colourless crystals of compound II were obtained after a period of three weeks. Melting point 509 K.
The 1 H NMR spectra of compounds I and II were recorded using a Bruker AC 400 MHz spectrometer (Fig. S3 in the supporting information). The compounds were dissolved in CDCl 3 using tetramethylsilane as an internal standard and chemical shifts () are stated in ppm. The imine proton resonated as a sharp singlet peak at 9.63 for I and at 9.73 for II, whereas the aromatic protons appeared as a multiplet at 6.69-7.74 for I and at 7.07-7.87 for II. The -NCH 3 protons of the aminoantipyrine unit appeared as a singlet at 3.08 for I and 3.16 for II. The two ethyl [-N(CH 2 -CH 3 ) 2 ] group protons in the benzylidene moiety of compound I appeared as a multiplet at 1.09-1.32 and 3.42-3.45. The methyl protons (C-CH 3 ) of the aminoantipyrine moiety appeared as a singlet at 2.49 for both I and II.
FT-IR spectra (KBr pellet) were recorded between 400 and 4000 cm À1 (Fig. S4 in the supporting information). The characteristic C N stretching mode is observed at 1578 for I, and at 1577 cm À1 for II, confirming the formation of the Schiff base compounds. The weak band at 3037 (I) and 3035 cm À1 (II), is assigned to the aromatic C-H stretching vibration. The peaks observed at 1290-1010 (I) and 1294-1124 cm À1 (II) are due to the C-H in-plane bending vibration of the aromatic rings. The bands obtained at 753-976 (I) and 757-954 cm À1 (II) are assigned to C-H out-of-plane bending vibrations. The asymmetric and symmetric stretching vibrations of the methyl group in the 4-aminoantipyrine moiety are observed respectively in the ranges of 3010-2970 (I) and 2940-2900 cm À1 (II). The strong peaks at 1650 (I) and 1644 cm À1 (II) correspond to the carbonyl stretching vibrations.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6. The C-bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.95-1.0 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.